1. Field
The disclosure relates to an electric disc brake. More particularly, the disclosure relates to an electric disc brake capable of compensating for volume variation in a cylinder caused by the movement of a piston.
2. Description of the Related Art
Different from a typical hydraulic disc brake, an electric disc brake employs a motor, which is operated by electricity, as a driving source for a driving unit that presses friction pads.
The electric disc brake according to the related art includes a disc rotating together with wheels of a vehicle, first and second friction pads arranged at both sides of the disc to press the disc, a pressing member moving back and forth to press the first and second friction pads, a motor generating a driving force, and a reduction unit amplifying the driving force of the motor to transfer the amplified driving force to the pressing member.
The reduction unit used in the electric disc brake according to the related art can be mainly classified into a parallel-axis type reduction unit and a coaxial reduction unit according to the arrangement between a motor shaft and the reduction unit.
In general, the parallel-axis type reduction unit includes an input-side gear coupled with an output shaft of a motor and an output-side gear engaged with the input-side gear and coupled with a screw connected to a pressing member.
However, the parallel-axis type reduction unit represents problems in that the gear connection structure is complicated, and the working friction occurs. Thus, if grease is boiled due to overheat of the brake, the parallel-axis type reduction unit may be broken by high pressure.